Telecommunications systems include a power plant having rectifiers for converting AC power to DC power for operating equipment. Associated with the power plant system is a controller for monitoring the rectifiers. The controller also communicates with local terminals as well as remote users via telephone line through a modem module. The operational status of the power plant may be communicated by the controller to either the local terminal or the remote users. A switching function is therefore needed to control communications between the controller, local terminal, or modem.
Such a switching function has been provided by mechanical relays in which contact closures create a communications path between the controller and local terminal or modem. However, mechanical relays exhibit several deficiencies in operation, particularly in a telecommunications environment. Relays utilize a large amount of current, are slow in operation, and are a source of mechanical failure, becoming xe2x80x9cstuckxe2x80x9d in an on or off position. Additionally, relays are relatively large in size, occupying a large area on a printed wiring board. Further, relays are generally expensive.
A need has thus arisen for a switching circuit for allowing a controller to communicate with a local terminal or modem that has low current consumption, switches at high speeds, and switches with low noise. Additionally, a need has arisen for a switching circuit that requires minimal space on a printed wiring board and which is cost effective.
In accordance with the present invention, in a telecommunications system having a controller, a local terminal, and a modem, a switch is provided. The switch includes a first buffer having an input and an output. The input of the first buffer is connected to the controller, and the output is connected to the local terminal. The switch includes a second buffer having an input and an output. The input of the second buffer is connected to the controller. The output of the second buffer is connected to the modem. Each of the buffers has an enabled state and a disabled state. The buffers are connected to the local terminal to receive an enable signal. When the first buffer is in the enable state and the second buffer is in the disabled state, the first buffer provides a communication path from the controller to the local terminal. When the first buffer is in the disabled state and the second buffer is in the enabled state, the second buffer provides a communication path from the controller to the modem.